(art, UK) Initialism of Royal Society of Arts. / Initialism of Republic of South Africa. / (cryptography) Initialism of Rivest-Shamir-Adleman (“an encryption algorithm”).

(Australia, hospitality) Initialism of Responsible Service of Alcohol (a qualification and permit for bar staff). / (aviation) Initialism of runway safety area.

plural of RSA

(mathematics) Any of the large semiprime numbers to be factored in the RSA Factoring Challenge, a competition from 1991 to 2007 encouraging research into computational number theory.

plural of RSA number

(UK, historical) Initialism of Royal Small Arms Factory.